1. Field of Invention
Aspects of the invention relate to a method for displaying a predetermined number of gray scales that are the same as those of obtained image data on an image display, such as a liquid-crystal-display panel provided in an image display apparatus, where the image display can display a limited number of gray scales.
2. Description of Related Art
A related art lightweight and low-profile display device, such as an LCD (liquid crystal display), can be mounted on a mobile terminal device, such as a mobile phone, a PDA (personal digital assistant), and so forth. Though full-color image data (eight bits for each of colors R, G, and B per each pixel (256 gray scales)) can be inputted for displaying an image on the above-described display device, the display often has to display gray scales of six bits for each of the colors R, G, and B (64 gray scales), for example, due to its limited performance. In this case, therefore, though the number of colors of the inputted image data is 16,777,216 in total (=256×256×256), the sum of displayed colors becomes 262,144 (=64×64×64).
In general, therefore, a method for interpolating the above-described shortage of colors simulatively by representing half-tone gray scales by a plurality of pixels through a dither process, an error-diffusion process, and so forth, is used frequently. For increasing the 64 gray scales to the 256 gray scales, for example, the dither process is performed, so as to interpolate three gray scales between steps of the 64 gray scales. However, since the number of gaps between the steps of the 64 gray scales (six bits) is 63, the number of gray scales obtained by the interpolation is only 253 (64+63×3). This gray-scale number does not agree with 256 perfectly and is three short of the required number. Subsequently, the number of colors becomes 16,194,277 (=253×253×253), which is 582,939 short of the total required number, when compared to that of the original data. Where the display apparatus can represent only five bits (32 gray scales) due to its performance, the gray-scale number becomes 249 (32+31×7), even though the above-described dither process is performed. Subsequently, the gray-scale number becomes seven short of the required number. Therefore, 1,338,967 colors are lost in total. Thus, where only one type of dither process is performed for the entire gray scales, so as to interpolate gray scales therebetween, the number of obtained colors does not perfectly agree with the number of colors of the original full-color image data.